Truth is tangled in the terror hype

As you weigh up the wisdom of a potential trip to the nearest high street in the light of the "Easter shopping suicide bombings plot", you might want to recall the "ricin plot" raids, which found no ricin; or the "airline plot" raids, which a jury decided last year did not feature any airlines; or the "cyanide on the tube" plots, which involved neither cyanide nor the tube. Given that Old Trafford is one of the reported potential targets of this latest alleged plot, you might also think back to the last time the stadium was named in relation to Islamist extremism - in 2004 - another alleged plot that turned out to be bunkum.

Clearly, however - and this is the difficulty behind every plot that has turned out to be hype - there are others that have not. There has been 7/7 and 21/7; the "doctors' plot" of 2007, which targeted nightclubs in London; and the Operation Crevice or "ammonium nitrate plot", which saw young Britons planning to bomb, among other targets, a giant shopping centre.

Overseas security sources with knowledge of the latest alleged plot describe it as aspirational, not operational. The prime minister says a big imminent attack has been averted, but no hard evidence of intent has as yet turned up. What we do know is that 12 people have been arrested, of whom 11 are Pakistani nationals.

Many previous plotters have been Britons who have travelled to Pakistan - most of them "pre-radicalised" in the UK - or local groups formed of relatively recent immigrants. So a group of Pakistanis sent to the UK is something different.

It is a return to a style of terrorist activity many thought had disappeared, much closer to that of the 1998 double bombing in east Africa or the 9/11 attacks than strikes such as those in Madrid or London, which depended predominantly on local volunteers who had been to terrorist camps in Afghanistan. If the British police are indeed dealing with a single group with a single purpose, that would indicate al-Qaida's capabilities after the damage done by the loss of Afghanistan in 2001 have been significantly regenerated.

One element seized on by newspapers has been the idea that this group came from Pakistan's tribal areas, where al-Qaida are based. This appears to be based on the name of one arrested man, Hamza Shinwari. The Shinwari are a tribe in eastern Afghanistan which stretches into western Pakistan around the Khyber Pass. A million strong, they are known as relatively moderate.

One lesson from the past decade is the extraordinary rapidity with which terrorist groups and tactics evolve. Analyses which break al-Qaida into neat categories - such as hard-core leadership, networked groups, individual freelancers and the ideology - are useful, but fail to capture the chaotic dynamism of contemporary Islamist militancy. We continue to look for linear answers to a phenomenon which is anything but straightforward in its form, its roots and the threat it poses.